The Haqqani network says a captive US soldier will not be harmed, even after the White House classified the Pakistan-based group as a "terrorist organisation".
One of the group's commanders said on Sunday that US Sergeant Bowe Bergdahl will not face retribution for the recent decision by the Obama administration.
But the group says it continues to plan attacks against US soldiers in Afghanistan.
The commander, speaking to journalists on condition of anonymity, denied that the Haqqani held Sergeant Bergdahl - believed to be the only US prisoner of war in the Afghan conflict - and said he was the captive of an Afghan branch of the Taliban.
He spoke out after speculation that the proscription of the Haqqani network would further risk the life of 26-year-old Bergdahl.
"I deny the remarks ... that this will endanger the life of the American soldier," the commander said.
"We are not cowards and we consider it as coward[ly] to harm prisoners."
US officials maintain that Bergdahl has been held by the Haqqanis since 2009. However, the Haqqani commander said he was with a group within Afghanistan.
"The American soldier is with the Emirate Centre ... The Americans also know it."
He said the Taliban leadership council had issued instructions to its commanders, and those of the Haqqani network, not to harm prisoners.
At home in Idaho, the soldier's father cautiously welcomed the assurances of the Haqqani commander.
"That's great news, but we're very careful about the information we digest," Bob Bergdahl told the Associated Press. He added that the commander's promise not to mistreat prisoners "was the position of the Emirate even before my son was taken prisoner".
The Haqqani are still reportedly planning to attack US and NATO soldiers in Afghanistan in retaliation for the "terrorist" designation.
Sirajuddin Haqqani, the organisation's military commander, is seeking permission from Taliban leader Mullah Mohammed Omar to stage a series of attacks against US forces in Afghanistan, said the unnamed Haqqani commander.
"He wants to carry out 80 to 100 attacks on US forces in Afghanistan and 20 attacks on other NATO members ... We
have our consultative and military council which plans attacks."
Threat to talks
The commander said that the Obama administration had been in touch with the Haqqani network last year as part of its efforts to broker a peace deal ahead of the withdrawal of US military troops from Afghanistan by the end of 2014.
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"[US Secretary of State Hillary] Clinton should have the courage to tell the Americans about their contacts and even talks with us," he said.
The US had previously resisted describing the Haqqani as "terrorists", reportedly because of fears such a move would jeopardise reconciliation efforts between the US government and armed groups in Afghanistan.
In the 1980s, Haqqani network founder Jalaluddin Haqqani was reportedly cultivated as a CIA asset and helped lead fighting against the Soviet-led forces then in Afghanistan. At around that time, US Congressman Charlie Wilson, who helped send millions of dollars to armed Afghan groups, referred to Haqqani as "goodness personified".
Clinton on Friday signed a report to Congress saying the network now met criteria for a "terrorist" designation, officials at the State Department said.
The report stated that the Haqqani network "meets the statutory criteria for designation as a foreign terrorist organisation", a US official told AP, as Clinton attended an Asia-Pacific Economic Co-operation summit in Vladivostok, Russia.
Relations with Pakistan
The Haqqani is reportedly affiliated to the Taliban and opposes the Afghan government; it operates on both sides of the Afghanistan-Pakistan border - but officials in Washington believe it is based in Pakistan's Waziristan tribal area.
Robert Grenier is a former director of the CIA's Counterterrorism Centre, as well as a former Islamabad station chief for the CIA.
He told Al Jazeera that, while he does not think there would be any immediate fallout between the US and Pakistan, it could have a long-term impact.
"The Pakistanis have been very careful to say 'look, this is an internal matter for the United States'," Grenier said. "The concern that I have, however, is for the future."
He warned that, in the event that Pakistan was shown to be providing material support to the network, "it would be very difficult to avoid designating Pakistan as a state sponsor of terrorism".
Meanwhile, the Taliban took to Twitter to denounce the US decision, saying there was "no separate entity... in Afghanistan by the name of Haqqani".
The Taliban tweeted that previous blacklistings of armed groups had no impact on operations and "this latest announcement will also be ineffective".
"This cowardly act of yours in which you enter mujahideen of Islamic Emirate into your so-called black list is indicative of your complete defeat and dismay," said the Taliban on Saturday.